There are people in the world who sleep only for three or four hours every night, even if they don't have to. Maybe they're crazy—or maybe they're genetically predisposed to sleep less. A new study in the journal Sleep reveals a gene mutation that allows people to remain functional even while clocking in fewer bedtime hours.

One hundred sets of twins were deprived of sleep for 38 hours and asked to perform tasks, so that researchers could isolate any genetic influence on need for sleep. Those who had certain mutations of the BHLHE41 gene could perform better with less shuteye and also chose to sleep fewer hours when they were allowed "recovery sleep". Even within pairs of twins, one twin who did have the gene mutation could differ in sleep need by an hour or so, and was much more resistant to the effects of sleep deprivation.

"This study emphasizes that our need for sleep is a biological requirement, not a personal preference," Dr. Timother Morgenthaler, president of the American Academy of Sleep Medicine, told The Telegraph. Maybe famous go-getters such as Benjamin Franklin and Margaret Thatcher weren't lying when they bragged about how little sleep they require. Even so, if you need seven hours for good health, don't be a martyr—maybe it's just not in the genetic cards for you.

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